1. Field of the Invention
This invention relates to ultrahard compacts, and more specifically to ultrahard compacts including ultrahard material integrally formed with a substrate. The invention also relates to improved methods for forming such ultrahard compacts.
2. Background Art
Ultrahard compacts typically comprise a body of ultrahard material bonded to a substrate. Examples of ultrahard materials include polycrystalline diamond (PCD) and cubic boron nitride (CBN). Substrates of ultrahard compacts typically are formed from a carbide material, such as tungsten carbide cemented with cobalt. Ultrahard compacts are well know for their mechanical properties of high wear resistance making them a popular choice for use as cutting elements in industrial applications, such as in cutting tools for machining and for subterranean mining and drilling tools.
Ultrahard compacts are typically formed by loading a can assembly with ultrahard material particles and substrate material and then subjecting the assembly to a high pressure high temperature (HPHT) pressing process that results in the sintering of the ultrahard material particles and bonding of the ultrahard material to the substrate. Methods for making ultrahard compacts are more fully described in U.S. Pat. Nos. 3,609,818; 3,743,489; 3,745,623; 3,850,591; 4,403,015; 4,954,139; and 6,610,095, the disclosures of which are expressly incorporated herein by reference.
Ultrahard compacts used for cutting tools and drilling tools are most commonly made in the form of a cylindrical member as illustrated in FIG. 1. The refractory metal containers used to form these compacts have cylindrical walls of uniform internal diameter along the length of the can. Ultrahard compacts produced in these types of cans have been found to have as much as a 20% to 30% difference in radial shrinkage between ultrahard material and substrate material when the compact is retrieved from the can after a pressing process. This has been found to be especially true for compacts formed with thicker ultrahard material layers, such as layers 1.0 millimeters (mm) or more in thickness. This is also particularly true for ultrahard compacts that are sintered in a high pressure high temperature apparatus known as a cubic press, although similar issues exist when compacts are formed using other types of presses, such as a belt press. The difference in radial shrinkage is believed to be due to differences in the shrinkage and consolidation of the different materials.
Ultrahard compacts, especially those with thick ultrahard layers, are typically tapered in form when recovered from the press, as illustrated for example in FIG. 4. The layer of ultrahard material 42 in these compacts 40 is tapered such that the ultrahard material nearest the substrate 44 (proximal interface 43) has the largest diameter and the ultrahard material furthest away from the substrate 44 has the smallest diameter. To obtain an ultrahard compact having a final desired uniform shape, these compacts 40 must be ground after the HPHT pressing process to bring the ultrahard material 42 and the substrate 44 to the same desired diameter 46 along the entire length of the compact 40. The thicker the body of ultrahard material 42 is on the substrate 44, the more pronounced the taper will be after the pressing operation, and the more grinding required to obtain a final uniform product.
Following conventional methods of manufacturing compacts as described above, the cost associated with centerless grinding of a compact with a diamond wheel to produce a final uniform product can be as much as 20% to 40% or more of the overall cost of the product, depending on the thickness of the ultrahard material body and the type and composition of the ultrahard material used to form a compact. Reducing the amount of centerless grinding required to manufacture an ultrahard compact of desired shape can result in a substantial cost saving due to a reduction in the number of grinding wheels required to finish products and in the time spent grinding and finishing products. Therefore, a method for manufacturing ultrahard compacts that reduces the amount of grinding and finishing required to obtain a final product is desired.